Comparison of blood lactate concentrations obtained during incremental and constant intensity exercise

Differences in blood lactate concentrations obtained during step-wise incremental and constant running exercise at the same intensities were investigated. In addition, the effect of endurance running at a constant intensity obtained by three different incremental modes (OBLA-4, 6 or 8 min) on the blood lactate concentration were studied. Eight firemen and six marathon runners performed: 1) three step-wise incremental running (IR) treadmill tests, each consisting of either 5x4, 5x6 or 5x8 min, and 2) six 50 min constant intensity running (CR) treadmill tests. Capillary hemolyzed blood was used for lactate determination. The blood lactate during the 5x4 min IR-test was 32% (p<0.001) lower for the firemen and 22% (p<0.001) lower for the marathon runners compared with the steady state concentration. These differences were diminished in both groups when the 5x8 min IR test was used. In the marathon group, constant intensity running at the OBLA intensities obtained by the 5x4, 5x6 and 5.8 min resulted in a lactate accumulation to a mean level of 8.1 mmol . 1(-1). Also, the marathon runners interrupted the exercise due to maximal perceived exertion after only 19+/-3, 26+/-4 and 30+/-6 min, respectively. In the firemen group, a majority of the subjects were able to complete the 50 min runs, despite a blood lactate accumulation to a mean level of 7.3 mmol . 1(-1) at the OBLA 5x4 and 5x6 min intensities. When OBLA 5x8 min intensity was performed in this groups, a steady state blood lactate concentration to a mean level of 5.3 mmol . 1(-1) occurred. It is concluded that step-wise incremental exercise with durations of 4 or 6 min will lead to a high risk of overestimating the maximal lactate steady state exercise intensity and the endurance running capacity.